1. Field of the Invention
The present invention relates to a multifunctional constant temperature refrigerator, and more particularly to a multifunctional constant temperature refrigerator with thermal carriers, in which heat is exchanged indirectly between an evaporator and the preserved stuff. The refrigerator of the invention can provide a freely and stably controllable temperature for the preserved stuff.
2. Description of the Prior Art
In order to preserve fruit and vegetables, they should be kept at a relatively low, constant temperature. Preserving fruit and vegetables minimizes their breathing intensity, blocks their metabolism, reduces as much as possible nutrient loss, slows the aging process, and permits their natural antibacterial, anti-disease and anti-decay capabilities to preserve their natural nutrition, freshness and flavor for a long period. Due to the biochemistry of plants' cells, these goals can only be attained by keeping the fruit and vegetables at a relatively low, constant temperature. Generally, in the course of naturally or artificially balancing biochemical heat, in addition to keeping fruit and vegetables to be preserved at an optimum temperature, the temperature variation should be minimized (i.e. within 0.5° C., and preferably within 0.1° C.) so as to limit the temperature variation of fruit and vegetables to about 0.1° C. Some lotus seeds that have been buried underground for over a thousand years can still bourgeon, grow and procreate, which is a vivid embodiment of the aforementioned principle (Principles of Seeds, P. 311–312, Science Press). To the contrary, if the environmental temperature is much lower than the appropriate temperature for the storage of fruit and vegetables, or if in the heating balance, fruit and vegetables encounter a lot of momentary changes at an extremely-low temperature to which ordinary temperature-measuring devices fail to measure, it is possible for fruit and vegetables to get frozen and damaged or physically disordered. As a result, the fruit and vegetables will speed up the decay when exposed to a normal temperature again. As is measured, the proper preservation temperature for fresh bananas is at 11° C. If a temperature to preserve bananas is lower than 10° C., or if bananas encounter repeatedly a momentary ultra-low-temperature, the bananas biological vitality will be destroyed, and then they turn black or harden, and finally have to be discarded. On the other hand, this also proves that the temperature control for preserving fruit and vegetables must conform to the biochemistry of plants' cells.
Some fruits, such as lichee, can regain their biological vitality after getting frozen once or twice. For preserving such fruits, the process requires two steps: first exterminating all attached harmful microorganisms at around −15° C. running on-end for several hours, and then keeping an appropriate constant temperature above 0° C. In fact, such requirements cannot be met at one compartment in a conventional refrigerator which uses an evaporator for directly heat-exchanging.
The preservation of meat is realized in a refrigerator through freezing to kill microorganisms that cause meat rotten from propagating. However, it is better for users to adjust the temperature within a certain range below 0° C. For example, if fresh meat is frozen at an environmental temperature of −7° C., it not only can keep a fairly long preservation period, but also is easy to be sliced for cooking in no need of further treatment. Today, even for technologically advanced refrigerators, it is the manufacturer who fixes freezing or cooling temperatures for respective compartments, and users cannot freely adjust, change or readjust the temperature set forth. Thus, it is inflexible and inconvenient in operation.
Since the first family refrigerator in the world was produced almost a hundred years ago, Either in the previously used serial recycling system or in the recently “separately recycling” technology that was first reported in Science Daily on Mar. 15, 2002, it is the evaporator that directly supplies a cooling source for the stuff to be preserved (equivalent through separate metal plates). As is well known, the evaporator of a refrigerator provides a cooling source below −20° C., which keeps most fruit and vegetables at a suitable preservation temperature for is above 0° C. Heat between the stuff and the refrigerator (absorbing biochemical heat of the stuff) is exchanged directly via air. Thus no matter what temperature-controlling technology is employed, momentary shocks of temperature variation cannot be controlled within 1° C. or 2° C. Thus, fruit and vegetables obviously cannot avoid the decay if they are preserved in the above-described refrigerator for a long period. The first thing for preserving fruit and vegetables is to avoid exchanging heat between great differences of the temperature, which is exactly the most prominent flaw of the present refrigerators.
Heat-exchanging between two contrasting temperatures can also make the exposed surface of fruit and vegetables lose water much faster than water transfer of the inside thereof. As a result, the surface of fruit and vegetables will crimple, which hinders normal metabolism of fruit and vegetable, and fails to achieve the result of keeping fruit and vegetables fresh in the real sense. If airtight plastic bags are used to wrap up stuff to be preserved, the vapor in the bag will shortly reach saturation, metabolic activities are forced to stop for water cannot be released, which will cause the stuff decayed.
Direct heat-exchanging between the evaporator and the frozen or cooled stuff can also cause the surface of the evaporator frosting repeatedly, which will increase heat resistance and definitely waste more power.
After all, there exists the drawback for the present refrigerators to keep fruit and vegetables fresh under the biochemical principles, which is the key to improve refrigerator technologies.